The belief that an intervertebral disc must degenerate
before it can herniate has clinical and medicolegal significance,
but lacks scientific validity. We hypothesised that tissue changes
in herniated discs differ from those in discs that degenerate without
herniation. Tissues were obtained at surgery from 21 herniated discs
and 11 non-herniated discs of similar degeneration as assessed by
the Pfirrmann grade. Thin sections were graded histologically, and
certain features were quantified using immunofluorescence combined
with confocal microscopy and image analysis. Herniated and degenerated
tissues were compared separately for each tissue type: nucleus, inner
annulus and outer annulus. Herniated tissues showed significantly greater proteoglycan loss
(outer annulus), neovascularisation (annulus), innervation (annulus),
cellularity/inflammation (annulus) and expression of matrix-degrading
enzymes (inner annulus) than degenerated discs. No significant differences
were seen in the nucleus tissue from herniated and degenerated discs.
Degenerative changes start in the nucleus, so it seems unlikely
that advanced degeneration caused herniation in 21 of these 32 discs.
On the contrary, specific changes in the annulus can be interpreted
as the consequences of herniation, when disruption allows local
swelling, proteoglycan loss, and the ingrowth of blood vessels,
nerves and inflammatory cells. In conclusion, it should not be assumed that degenerative changes
always precede disc herniation. Cite this article:
We present the histological findings of bone retrieved from beneath the femoral components of failed metal-on-metal hip resurfacing arthroplasties. Of a total of 377 patients who underwent resurfacing arthroplasty, 13 required revision; for fracture of the femoral neck in eight, loosening of a component in three and for other reasons in two. None of these cases had shown histological evidence of osteonecrosis in the femoral bone at the time of the initial implantation. Bone from the remnant of the femoral head showed changes of osteonecrosis in all but one case at revision. In two cases of fracture which occurred within a week of implantation, the changes were compatible with early necrosis of the edge of the fracture. In the remaining six fractures, there were changes of established osteonecrosis. In all but one of the non-fracture cases, patchy osteonecrosis was seen. We conclude that histological evidence of osteonecrosis is a common finding in failed resurfaced hips. Given that osteonecrosis is extensive in resurfaced femoral heads which fail by fracture, it is likely to play a role in the causation of these fractures.
